The invention concerns a controllable microswitch comprising a closed cavity having a plurality of contact electrodes, a movable switch body capable of making and breaking an electrical connection between the contact electrodes, and a plurality of control electrodes capable of generating an electrical field to control the position of the switch body. The invention moreover concerns methods of making such a microswitch. Finally, the invention concerns use of a microswitch for power regulation of systems connected to an electrical power source and for remote-controlled connection and disconnection of an apparatus in an electrical mains supply.
A need is being created for an "intelligent" installation system where the user can turn on and off selected electrical appliances at specific times all around the clock via a central computer or via central logic. The user will obtain greater convenience and flexibility, and the supplier of electricity can obtain a better control of the load in the mains supply--particularly during peak load periods--through direct control or through differentiated electricity prices.
The mains voltage to the consumer is up to 230 V, and in traditional contact breakers it is therefore necessary to maintain an insulation distance of about 2 mm between the live parts internally in the contact breaker owing to arc formation. This electrode distance may be calculated by means of Paschen's law.
Micromechanical relays are known and are described e.g. by Gretillat et al. in an article in "Proceedings of the 1994 IEEE Micro Electro Mechanical System", January-February 1994, p. 97-101, by Hackett et al. in the article "Smart Materials Fabrication and Materials for Micro-Electro-Mechanical Systems" edited by Jardine et al. and in "Materials Research Society Symposium Proceedings", vol. 276, Apr. 28-30, 1992, p. 241-252. These relays are designed to connect and disconnect small currents and voltages, the use being low power electronics, i.e. currents in the range around 1 mA and voltages in the range around 10 V.
GB-A-2 095 911 defines an electrical switch having a tiltable switch body, where the position of the switch body is controlled by means of an applied electrical field. The switch cavity of the switch may be under vacuum or filled with an inactive gas, thereby preventing the control voltage from causing flashover.
JP-A-4-58428 and JP-A-58429 disclose an electrostatic relay produced by semiconductor technology. The relay has an evacuated switch housing with a tiltable switch body, e.g. of palladium.
DE-C-42 05 029 discloses a micromechanical relay which operates by means of electrostatic control. The switch housing of the relay accommodates an armature through which the contact electrodes may be connected with each other. The armature is formed by a resilient arm on which a conducting web has been applied.
DE-A-43 05 033 and DE-C-42 05 340 both disclose a relay structure in which armature arms are replaced by an armature plate on which the conducting web has been applied. The armature plate is suspended resiliently by means of connecting bridges at the corners of the plate.
However, in these switches having a switch body arranged in a closed cavity, it is a problem that the contacts provided on the switch body have a relatively small area and can therefore just connect low voltages and currents like the above-mentioned micromechanical relays. Further, mechanical wear may occur owing to the movement of the switch body at the points where it is connected to the fixed part of the switch.
SU-A-462 228 discloses another type of electrostatic relay where the switch body is not arranged in a closed cavity. Instead, a contact is arranged on a diaphragm-like member which is fixed between two end pieces. As no closed cavity is involved, this relay does not allow the contacts to be placed under vacuum or in an inactive gas, which is absolutely necessary if small dimensions are to be combined with high voltages. Further, this relay, too, has small contact areas and thus relatively great contact resistances, so that just small currents can be connected. Finally, the connection to the actual contact in this relay takes place by means of a tape connector, which cannot be used with small dimensions and closed cavities.